% Drawing a graph
% Author: Stefan Kottwitz
% https://www.packtpub.com/hardware-and-creative/latex-cookbook
\documentclass[border=10pt]{standalone}
\usepackage{tikz}

\usepackage{verbatim}
\usetikzlibrary{arrows,shapes}

\tikzstyle{vertex}=[circle,fill=black!25,minimum size=20pt,inner sep=0pt]
\tikzstyle{selected vertex} = [vertex, fill=red!24]
\tikzstyle{edge} = [draw,thick,-]
\tikzstyle{weight} = [font=\small]
\tikzstyle{selected edge} = [draw,line width=5pt,-,red!50]
\tikzstyle{ignored edge} = [draw,line width=5pt,-,black!20]

\begin{document}
\begin{tikzpicture}
\draw [->] (0, 0) node [vertex, left] {B} -- (1, 1) node [vertex,right] {C};
\draw [->] (0, 0) -- (1, -1) node [vertex, right] {D};
\draw [->] (1.72, 1) -- (2.72, 0) node [vertex,right] {A};
\draw [->] (1.72, -1) -- (2.72, 0);
\draw [->] (3.44,0) -- (4.44,0) node [vertex, right] {B};
\draw [->] (1.72, 1) -- (2.72, 1) node [vertex, right] {B};
\draw [->] (3.44, 1) -- (4.44, 1) node [vertex, right] {A};
\end{tikzpicture}
\end{document}